Contact lenses need to be cleaned/disinfected in order to remove microbes, proteins, lipids and other debris from the surfaces of the lenses. Two classes of contact lens cleaning/disinfecting solutions are commonly available for use with soft contact lenses: the class of the multipurpose disinfecting solutions (MPDS) and the class of the hydrogen peroxide solutions.
Concerns over the use of hydrogen peroxide systems involve ocular toxicity and recontamination. Firstly, hydrogen peroxide is harmful for the eyes. Therefore, hydrogen peroxide systems need to neutralize the hydrogen peroxide solutions through a catalyst prior to lens wear. Premature removal of lenses from the solution prior to full neutralization may lead to ocular toxicity. Some systems that may adequately provide means for neutralizing the hydrogen peroxide fail with respect to the second concern. Secondly, hydrogen peroxide systems are not storage solutions. Following neutralization, hydrogen peroxide solution becomes water (and O2 which leaves the cup through little holes in the cap). Water typically fails to provide contact lenses with adequate protection from contamination when stored for selected periods of time. Lenses should generally be removed from the neutralized solution and worn relatively soon thereafter. Long delays in removing the lenses from the cup, which now contains unprotected water, may cause re-contamination of the lenses with opportunistic microbes. In contrast, a MPDS solution can act as a good storage solution but typically has less disinfecting power against certain fungi and especially fungi cysts.
There are two commonly available H2O2 systems: the one-step H2O2 system and the two-step H2O2 system. In the one-step H2O2 system, the catalyst neutralizes the hydrogen peroxide solution from the start of the process, while in the two-step H2O2 system, the neutralizing catalyst is added at the end of the disinfection phase. While the two-step H2O2 systems were shown to be more effective disinfecting solutions than the MPDS and the one-step H2O2 systems, two-step systems tend to fall out of favor mainly due to the need for the extra step needed to neutralize the H2O2 solution. Furthermore, conventional two-step systems typically fail to provide a safe system to avoid ocular toxicity and recontamination. Although great strides have been made in contact lens cleaning systems, considerable shortcomings remain.